Editing Turtle (section)

===Limbs and locomotion===

Due to their heavy shells, turtles are slow-moving on land. A [[desert tortoise]] moves at only {{cvt|0.22|–|0.48|km/h|abbr=on}}. By contrast, sea turtles can swim at {{cvt|30|km/h|abbr=on}}.<ref name=Firefly/> The limbs of turtles are adapted for various means of locomotion and habits and most have five toes. Tortoises are specialized for terrestrial environments and have column-like legs with elephant-like feet and short toes. The [[gopher tortoise]] has flattened front limbs for digging in the substrate. Freshwater turtles have more flexible legs and longer toes with [[Webbed foot|webbing]], giving them thrust in the water. Some of these species, such as [[snapping turtles]] and [[mud turtle]]s, mainly walk along the water bottom, as they would on land. Others, such as terrapins, swim by paddling with all four limbs, switching between the opposing front and hind limbs, which keeps their direction stable.<ref name=Firefly/>{{sfn|Orenstein|2012|p=38}}

[[File:Green Sea Turtle swimming.jpg|thumb|[[Sea turtle]]s have [[streamlined]] shells and limbs adapted for fast and efficient swimming.<ref name="Davenport 1984"/>|alt=Marine turtle swimming]]

Sea turtles and the [[pig-nosed turtle]] are the most specialized for swimming. Their front limbs have evolved into flippers while the shorter hind limbs are shaped more like rudders. The front limbs provide most of the thrust for swimming, while the hind limbs serve as stabilizers.<ref name=Firefly/>{{sfn|Orenstein|2012|pp=38–40}} Sea turtles such as the [[green sea turtle]] rotate the front limb flippers like a bird's wings to generate a propulsive force on both the upstroke and on the downstroke. This is in contrast to similar-sized freshwater turtles (measurements having been made on young animals in each case) such as the [[Caspian turtle]], which uses the front limbs like the oars of a rowing boat, creating substantial negative thrust on the recovery stroke in each cycle. In addition, the streamlining of the marine turtles reduces drag. As a result, marine turtles produce a propulsive force twice as large, and swim six times as fast, as freshwater turtles. The swimming efficiency of young marine turtles is similar to that of fast-swimming fish of open water, like [[mackerel]].<ref name="Davenport 1984">{{cite journal |last1=Davenport |first1=John |last2=Munks |first2=Sarah A. |last3=Oxford |first3=P. J. |title=A Comparison of the Swimming of Marine and Freshwater Turtles |journal=Proceedings of the Royal Society of London. Series B. Biological Sciences |volume=220 |issue=1221 |date=February 22, 1984 |issn=0080-4649 |doi=10.1098/rspb.1984.0013 |jstor=35758 |pages=447–475 |bibcode=1984RSPSB.220..447D |s2cid=84615412 }}</ref>

Compared to other reptiles, turtles tend to have reduced tails, but these vary in both length and thickness among species and between sexes. [[Snapping turtles]] and the [[big-headed turtle]] have longer tails; the latter uses it for balance while climbing. The [[cloaca]] is found underneath and at the base, and the tail itself houses the reproductive organs. Hence, males have longer tails to contain the penis. In sea turtles, the tail is longer and more [[prehensile]] in males, who use it to grasp mates. Several turtle species have spines on their tails.{{sfn|Orenstein|2012|p=40}}{{sfn|Franklin|2011|p=18}}